PSLY 4210/5210 !Comparative Animal Physiology !Spring 2010! !Respiratory Pigments!
Respiratory Pigments! Types of Respiratory Pigments! High molecular weights (105 to nearly 107 D)! !Hemocyanin - gastropods and cephalopods, Conjugated proteins - proteins complexed w/ crustaceans, arachnids, and horseshoe crabs! other organic molecules or metal ions (Fe2+ or Cu-containing protein, MW 1-7 million D! Cu2+)! One hemocyanin molecule contains two Cu atoms and can combine with 1 O2 molecule! Color produced by these complexes! Blue in deoxygenated state, colorless or white in oxygenated state! Pigment is not oxidized by O , it is oxygenated (reversible 2 Never present inside cells, but always in suspension in blood! reaction)! !Hemerythrin - sipunculids (peanut worms), Necessary because of low solubility of O2 in polychaetes, priapulids, and branchiopods! aqueous solution (about 0.3 ml O /100 ml)! 2 Fe-containing protein, MW about 100,000 D! Allow transport of molecular oxygen, pickup of O2 at sites One hemerythrin molecule contains several Fe atoms and each O2 of high O2 tension and deposition at sites of low O2 tension! molecule can combine with 2 or 3 Fe atoms! Allow blood to carry a much greater quantity of O 2! Brownish in deoxygenated state, purple in oxygenated state! Allow quick removal of O2 from respiratory surfaces, thus Contained within coelomocytes that circulate within the coelomic maintaining a concentration gradient down which O2 can fluid! diffuse!
Types of Respiratory Pigments! Types of Respiratory Pigments! !Chlorocruotin - two families of marine !Hemoglobin (Hb) - all vertebrates and many invertebrates polychaetes (Serpulidae and Sabellidae)! (most annelids, nemerteans, phoronids, and echiurids)! Fe-containing protein, MW 68,000 D in humans. Composed of Fe-containing protein, MW about 3 million D! two pairs of polypeptide chains (α and β-Hb). Size ranges from 17,000 D to 3,000,000 D (annelids).! Similar structure to hemoglobin, except that in Similar in structure to cytochromes, and thus is also found in the heme group one vinyl group is replaced by a plants! formyl group! Contains four heme groups, each of which can combine with one O2" As with hemoglobin, one O2 molecule combines" molecule, when all four heme groups are complexed with O2," with each of the 4 heme groups! the molecule is said to be fully saturated! Dark red in the deoxygenated state, bright red in the Green in both deoxygenated and" oxygenated state! oxygenated states! May occur within RBCs or in suspension in blood. Effectiveness greatly increased when packed into cells, as is Occurs in suspension in blood! true of most vertebrates!
Figure 23.1 The chemical structure of hemoglobin (Part 1) Figure 23.1 The chemical structure of hemoglobin (Part 2)
Topic 13 - 1! PSLY 4210/5210 !Comparative Animal Physiology !Spring 2010! !Respiratory Pigments!
Figure 23.2 Human developmental changes in the types of globins synthesized for incorporation Figure 23.3 The distribution of hemoglobins in animals into blood hemoglobins
Figure 23.4 A typical oxygen equilibrium curve for human arterial blood presented in two different ways Functions of Respiratory Pigments!
At a given pH, the amount of O2 that a given quantity of
respiratory pigment can pick up depends on PO2 (usually in mm Hg), and the loading of the pigment is given in
percentage of saturation with O2! These relationships are" called oxygen dissociation" curves. The s-shape allows"
more O2 to be delivered a"
a given PO2 ! Slight changes in PO2 permit" a relatively large amount of" ’ O2 to be released (at PO2 s" typical of tissue cells)!
’ At higher PO2 s (typical of" respiratory surfaces), pigment" is completely saturated!
Figure 23.7 Respiratory pigments display hyperbolic or sigmoid oxygen equilibrium curves depending on whether they exhibit cooperativity in O2 binding Figure 23.8 A diversity of blood oxygen equilibrium curves
Topic 13 - 2! PSLY 4210/5210 !Comparative Animal Physiology !Spring 2010! !Respiratory Pigments!
Figure 23.9 How to measure P 50 Functions of Respiratory Pigments!
Half-saturation pressure is the PO2 at which a respiratory pigment is only half-saturated with O2! Pigments with a lower half-saturation pressure have a higher affinity
for O2! For example, myoglobin has a" half-saturation pressure of" about 6 mm Hg, compared" with human hemoglobin’s 34" mm Hg. This allows myoglobin"
to remain complexed with O2," while the O2 of hemoglobin is" 98% dissociated! Myoglobin’s dissociation curve" is thus not sigmoidal, and" resembles the hyperbaric curve" on the previous slide! This is because myoglobin has only one protein chain and one heme group, and can thus combine with only one O2!
Figure 23.10 The Bohr effect: Affinity for O2 decreases as pH decreases or CO2 partial pressure Environmental Effects on" increases Respiratory Pigment Function!
In hemoglobin, the interaction of one heme group with an O2 molecule increases the affinity of the other heme groups! Since the 3-D structure of hemoglobin suggests that the heme groups are
widely separated, it is though that the combination of O2 with one heme group affects the entire Hb molecule shape!
O2 dissociation curves also affected by temperature, blood pH,
and blood PCO2! Low pH or high PCO2 generally shift the dissociation curve to the right
(Bohr effect). These effects are slightly different, although a high PCO2 does produce a lower blood pH!
This important in O2 transport, in that the PCO2 in the capillaries around active tissues is elevated and the blood slightly acid. Under these
conditions, a shift to the right facilitates O2 unloading! Explains why sudden shifts in temperature, or decreased pH from acid deposition, can kill aquatic animals!
Environmental Effects on Respiratory Pigment Function! Figure 23.11 The Bohr effect typically enhances O2 delivery in an animal
Effects of blood pH and blood
PCO2 on O2 dissociation curves of human hemoglobin!
Effects of pH and temperature on O2 dissociation curves of horseshoe crabs. Note the reverse Bohr effect for pH.!
Topic 13 - 3! PSLY 4210/5210 !Comparative Animal Physiology !Spring 2010! !Respiratory Pigments!
Figure 23.12 The Root effect in eels: Acidification lowers the oxygen-carrying capacity of Reverse Bohr Effect! hemoglobin !Why would an organism have a reverse Bohr effect and high O2 affinity?! Actually, a given pigment may not exhibit the Bohr effect in a given animal, but all of the respiratory pigments have been shown to exhibit this behavior, ’ especially at high PCO2 s! Typical of animals that live in stagnant, low O2 environments! Reverse Bohr shift increases the loading capacity of blood under these conditions! In the case of horseshoe crabs, it is to provide enough O2 for reproduction. ! Long copulatory period in shallow bays!
High temperatures low dissolved O2, etc.!
Figure 23.13 An increase in temperature typically causes a decrease in O affinity 2 Other Effects on O2 Affinities! O2 affinity decreases at low salinity, probably due to conformational effects on pigment proteins!
O2 affinity of hemoglobin is decreased by phosphate compounds in vertebrate blood cells: ATP, GTP, diphoshoglycerate (DPG), inocetyl pentaphosphate (IP5)! Fishes: high GTP! Reptiles: high ATP! Birds: high IP5! Mammals: high DPG!
These phosphate compounds increase O2 loading, and can increase or decrease O2 unloading!
Figure 23.14 The normal P50 of human hemoglobin within red blood cells depends on a normal Figure 23.15 A decrease in the O2 affinity of hemoglobin can aid O2 delivery to the systemic tissues intracellular concentration of 2,3-DPG when the O2 partial pressure in the breathing organs remains high
Topic 13 - 4! PSLY 4210/5210 !Comparative Animal Physiology !Spring 2010! !Respiratory Pigments!
Figure 23.17 Blood O2 delivery in an octopus: Even at rest, octopuses have almost no venous Figure 23.16 Blood O2 transport in rainbow trout in relation to exercise reserve
Figure 23.18 The O2 affinity of the hemoglobin in the whole blood of primates is a regular function Figure 23.19 When water fleas are transferred to O2-poor water, their O2 transport system of body size undergoes rapid acclimation because of altered gene expression
CO2 Transport! Hemoglobin and CO2 Transport! CO produced by tissue cells is transported to the lungs – 2 HbNH2 + CO2 ⇔ HbNHCOOH ⇔ HbNHCOO! or other respiratory surfaces for excretion! Where NH2 represents the amino groups of the Only small amounts of CO2 are in solution in the blood because of reactions that occur within the plasma, or amino acids of the hemoglobin (the complex is within erythrocytes of vertebrates! known as carbaminohemoglobin)! At the respiratory surface, CO diffuses from CO2 in aqueous solution forms carbonic acid (H2CO3), a 2 reaction speeded by the enzyme carbonic anhydrase, the blood into the air or water. Carbonic which is found in the blood of many animals (in anhydrase catalyzes the reverse reaction and vertebrates it is mostly within the erythrocytes)! aids in forming CO2, which can be eliminated! + – Carbonic acid can dissociate into H and HCO3 , and Direction of the reaction depends on PCO2: these bicarbonate ions can then enter the acid-base where CO is low (as near the respiratory regulating mechanisms! 2 exchange surfaces) H2CO3 is split into H2O and However, about 15-20% of the CO2 reacts with CO2 , and the CO2 move down its hemoglobin! concentration gradient to the exterior!
Topic 13 - 5! PSLY 4210/5210 !Comparative Animal Physiology !Spring 2010! !Respiratory Pigments!
Figure 23.22 The processes of CO2 uptake by the blood in a systemic blood capillary of a vertebrate Figure 23.20 Carbon dioxide equilibrium curves
Figure 23.23 Normal blood pH is a temperature-dependent variable
Topic 13 - 6!